The objective of this work is a biophysical characterization of arterial wall with respect to its permeability to solutes of differnt sizes and ionic charge. Low density lipoprotein, the accumulation of which wthin the arterial wall, leads to atherosclerosis will be included in the solutes to be tested. The permeability parameters to be determined are: hydraulic conductivity, solute permeability coefficients and solute reflection coefficients. An analysis of the results will indicate the overall porosity of arterial wall and its selectivity towards low density lipoprotein. Emphasis will be placed on the permeability properties of the endothelium - intimal layer. Endothelial integrity, which may be difficult to maintain in vitro, particularly using previous techniques, will be monitored by the silve-nitrate stain microscopy technique and attempts will be made according to the current state-of-art to maintain endothelial integrity. Vasoactive agents like angiotensin and norepinephrine have been suggested to be involved in accelerating lipid accumulation by transiently forming endothelial gaps (the 'trap-door' effect). One of the objectives of the proposed work will be to characterize the effects of vasoactive agents on the porosity and selectivity of the aortic wall to molecules of different sizes. Agents like angiotensin II, nor-epinephrine, theophylline and Ca ions - antagonists will be used at concentrations which are optimal in their effect on aortic smooth muscle cell relaxation and contraction.